1. Field of the Invention
This invention pertains to lamp dimming circuits and more particularly to such circuits that provide regulation as well as dimming and provide IES square law compensation for incandescent lamps at various light intensity settings.
2. Description of the Prior Art
Complex control and regulation of incandescent lamps are desirable in many applications, but none may be more critical than the control and regulation of such lamps employed in stage lighting. It is quite common for there to be a plurality of lamps at different locations and a plurality of banks of lamps to achieve intricate gradations of light intensity for many special effects.
Light control systems in the past have recognized the desirability of utilizing a compensation network in accordance with the IES square law compliance curve. The reason for having such compensation is that the human eye does not respond linearly to changes in light intensity, but in accordance with a square wave response. Systems in the prior art have applied line voltages through networks to apply such correction. Such systems waste energy, however, by using components that are not useful in light production to absorb part of the applied energy. Also, the aging of components distorts the response. Furthermore, the range of operation where the lights are operated at their dimmest has been extremely difficult to regulate using prior art systems, since snap-on and snap-off of the lights occurs. That is, there is no gradual and controlled lighting from off to dim. Such light jumps are distracting to both audiences and performers alike and can destroy the careful mood settings that are so important.
Finally, separate line regulators are usually employed apart from load sensing regulators to compensate for possible variations in applied source voltages. That is, the prior art systems just discussed are not able to distinguish from an intentional decrease in applied voltage to a lamp load from an unintentional decrease because of an uncontrolled line voltage variation drop.
Therefore, it is a feature of the present invention to provide a common circuit that achieves improved line and load regulation in an incandescent lamp dimmer.
It is another feature of the present invention to provide an improved incandescent lamp dimmer wherein IES square law compliance correction is developed by sensing the voltage across the lamp, rather than just applying it in conjunction with the power applied to the lamp.
It is still another feature of the present invention to provide an improved line and load regulation in an incandescent lamp dimmer by using voltage sensing of the load voltage, applying such sensed voltage to an IES square law shaping network and using the voltage after such network for regulation purposes.
It is yet another feature of the present invention to provide an improved IES square law shaping network useful in a control path of an incandescent lamp dimmer and regulation circuit wherein the network charges and discharges at different times and at different rates to achieve non-linear correction.
It is still another feature of the present invention to provide an improved incandescent lamp dimmer employing an integrated circuit operational amplifier as a summing amplifier and employing a pulse generator controlled by a Model 555 timer.